Clarification of liquids



J. w. Hoon CLARIFICATION OF LIQUIDS Filed Aug. 3, 1940 .DIREKT/0N 0f l/V r N m MW. d /mm F n M 0 0 a E Jf/ V n r N m W Y @M m m n my M 7 m .J l Y Allm/ 5 M .w B 1 f R ,.:YS Z my m w f n in |IW a .M m W W l u i P u im M f w wm m n L F. m l H I||P| Il |||||4 M 6 H IML l L T m W ma w 7./.IIEIII II'I l. m a m M 9 z c @m .!|.l|.b|.|.i/ M m w 5 me m 9 a 7 e 50 im n H MM. 5 F Pm C May 30, 1944.

rnes'dmsyaaisup cmiurrca'noN or uQUms John W. Hood, Ridgewood, N. J., assignor to Ac'- co, Incorporated, Bloomdeld, N. J., a corporailon of New Jersey Application August 3, 1940. Serial No. 351,214 (ci. 21o-2:)

5 Claims.

This invention relates to the clarification of water. sewage and various waste liquors by chemical coagulation and sedimentation, and particularly coagulation by a chemical electrolyte such as aluminum sulphate or an iron salt, ferrie sulphate, ferrous sulphate or ferric chloride.

The object is to bring the Water or sewage into condition to make most eillcient use of the chemical coagulant and attain coagulation giving an emuent liquid of uniform near zero turbidity in the following tank or clariiler. q

The procedure comprises the introduction of q carbon dioxide, CO1, by means of a blower or compressor, to ."raw sewage or untreated water or other liquor prior to chemical treatment for clariilcation, for the purpose of precarbonating the untreated liquid and so adjusting the chemical balance of the sewage or water structure, that substantial economy will be effected in the amount .l oi sewage and the like a definite minimum requirementoi! electrolyte exists in any sewage or water.` This is apparently due to surface adsorption oi the dissolved organic and colloidal matter. When this demand has been satisfied, coagulation yis successful, precipitation from solution otthe In the accompanying drawing illustrating the invention Fig. l is a diagram showingla typical layout for the liquid clarification of this invention, and

Fig. 2 is a reproduction ofthe calcium carbonate solubility equilibrium curve.

In the system of this invention the liquid to be coagulated is passed into a primary clarifier 5 unless already suillclently clarified. When clarified it has carbon dioxide diiused and distributed in diffuser 6 in it so as to come thoroughly into contact with all parts of the liquid and the supply of carbon dioxide is such as to reduce the pH to about 5.9 to 6.1. To attain this a small 'portion of the treated liquid is drawn oil' from a point 1 subsequent to the carbon dioxide diduser B andpassed through a pH meter I connected at 9 to control the supply i0 of carbon dioxide automatically to maintain the pH `within the desired limits. It is important that this DH control be substantially continuous. the control meter l receiving a constant supply from the treated liquid and exercising a constant control over the supply dissolved matter being complete, resulting in the y clariilcation of the sewage.

However, it has been noted that an unfavorjable chemical balance daily and seasonally intervenes in most plants to prevent proper precipitation at this juncture, and modification of the balance to a favorable zone invariably involves large increase in the amount of chemical serving as 'the electrolyte. This is a costly proceeding in terms of chemical consumed.

A substitute for the additional chemical being usedL for chemical balance adjustment has been sought, but it was discovered that. strong acids were not always dependable and had a bactericidal eilecton the biological entities by which the anaerobic digestion of sewage sludge is promoted and the conversion oi complex volatile organic matter to stable chemical elements accomplished.

Laboratory determinations and plant observations have shown that carbon dioxide and the resulting carbonio acid H2O CO: HzCOs) 1 Water Carbon Carbonic dioxide acid life involved in the digestion process.

combustion producing the carbon dioxide.

oi the carbon dioxide tothe diffuser. In practice the DH meter used may be a Coleman or Cambridge or other standard pH meter connected to a valve in the carbon dioxide supply so as to accurately vary the supply instantaneously at all times. The Coleman meter referred to is that of the Coleman Electric Co., Inc. oi Maywood, Illinois, and the Cambridge meter is that of the Cambridge Instrument Co.. Inc., Grand Central Terminal. New York, N. Y. 'In some instances it may be more economical to vary the amount of The diii'useimay be of any desired eilicient type such as the porous stone-type manufactured by the Norton company and the Carborundum company.

The carbon dioxide treated liquid from the diiIuser with a pH of about 6.0 then has introduced into it and mixed with it atl! an accurately measured amount oi' chemical electrolyte such as aluminum sulphate or a mixture of iron salts or the like, the quantity of the chemical being controlled in accordance with the turbidity of the liquid at a point Il immediately after segregation. Toaccomplishthis segregation the chemically treated liquid is run into a ilocculaior I4 preferably of the mechanical type, after which the liquid may be run oi to a secondary clarifier i5 at a point I6 in the occulator" closely following the attainment of segregation, and part of the liquid is continuously drawn off at i3 and clariiied by sedimentation and passed to a turbidimeter il measuring the turbidity by directing light into a passing current of the liquid and measuring the resulting illumination in a line at right angles to the original beam and correspondinsly and continuously controlling the supply of 'the cccgciccing chemical.r The iurbidimetcr i1 yis thingftoo vit is only necessary to add kwater as will-enable thercarbon dioxide and chemical' treatment to bringthe final co'nditionof the efiluent the desired amount, below the vCox calcium setto givea supply of chemical `from chemical feeder `I8 according to the desired clarityof the effluent from the flocculator'fory instance, ,de'

pending 'upon whether-this Aefiluentis to Abecleisir or crystal clear. i In practice-the controlling instrument I1 maybe aNo. 1l turbidity meteroi the Coleman Electric Company of Maywood! Illinois.

' The eiect ofthe addition of the aluminum sulphate or other similar chemical electrolyte is n reduce the alkalinity and` at the same time to some degree also lower the pHpandI have foundthat to' pH as ordinates and alkalinity as abscissae whichfwill be: belovi'the calcium carbonate 'solu' bility-.equilibrium curve as determined by "Charles RlvCoxiifhiS pamphleVWater supply '-cont'rol', I

f Bulletin 22;'f1939yof the'New' York. State Depart- For 4ay clear ment `of VHealth,"pages 1139-1'47.` eiiluent, this pointishould be 1.0 pH- or more below It is possible atall times-` to check theoperation other acidsjhave been used in earliertreatments. The acidity provided by the volatile car-` bon dioxidebeing temporary disappears lprior'to digestion and v1reduces oravoidsjaltogether the "usefor; limeasafcorrectiye. Thisvis-'al'so true in water purication i wherev any' permanent acidity l after coagulation is undesirable.

r4With the continuous controls ofv the'rp'resent i proc'essfthere is very close uniformity in results,

theclariiledeilluenb from the secondary clarier beingveryfeven inv composition in spite of Wide variationsiri they-rawliniluent and all this is acl ,A complished under conditions insuring effective` y in order to obtain a clear eflluentfrom the floccua c jlatol', it is necessary to arrive at a point plotted thiscal'ciumr carbonate solubiltygequilibrium curve and 1.25 pH Tor more below -for crystal.y clarity.

termine iust'wherethis -efiluent is withrelationto the cal'ciumcarbnate equilibrium'scurve.. `A riythe'pI-I'to within the desired riainge,4 the-alkalinity at this point may be stili so high as'to preclude the successfulv treatment with the chemical electrolyte because ofthe excessive' quantities called for and th'resulting Vco'ri'ipli'cations caused by such excess. In fsuchcase I5 have foundzit possible to bring the raw liquid within efllcienttreatmentvby fdiliiting it with a source of water having asuiii-V alkalinity. To accomplish this:

such a quantity of the ciently lower pH nearftc" this Vequilibriumcurveis boundtob'e relativelycloudy and'les's satisfactorylfand" the cloudiness increase'sin objectionable manner Vas thejcurveis approacheii.` l. f

' Itfsomewhatffreque tly occurs that the raw i regla'tio'n""of*thev entire procedure and with a operator.

The" calciunricarbonate solubility equilibrium. curve" referred`- tofin the foregoing jspeciii'catin andtric-'followingclaims `is that" hcw'n ifi Eig; 2 l

fof thclvacccmpanyinz drawing. r I'clairn: n 1.y A` coagulation process "oori'iprising'` ldiiusing carbon dioxide in vthorough"contactfwith "a supply f teriand` having" aflpH valuenotlessfthanthejpI-I" value'at which 'calcium' "carbonate-'can fexistfin equilibrium in said 4'liquid continuin'gsaid treatequilibrium said liquid, terminating, said` cafrbon dioxide treatxiient andf'thenjadding aicoa'gu-f lant acting further .tolower the plrvalue' of .said

'libriumin. said `liquid and. effective "to f cause coliqu'i'dtodesiredidegree -A '2.'v Theprocess'as setl "and the coagulant are continuousjthe carbon -dioxide is difrusjed'f in thc-iiquid in advance' cfihc addition of the vcoagulantand* ina'mount reduccarbonate solubilityequilibrium 4curve 'asf above be drawn off from vthe .clarified eilluent ofthe secondary clarifier or from such other vpartof the purification system as is most efficient and practical as a' source of dilution.

- In addition tothe `saving in chemicalsthe process in using the volatlecarbondioxide to de-' press the pH avoids imparting a permanentacidity to the liquid. and thus dispenses with the necessity of later correcting this acidity where higherwpH "values arev subsequently required. For instance,

are passed on to a digester. this coagulum bearing organic niatter should vnot be at all strongly Y v explained. The dilution water may,.i`or instance,

toapo' "t below'said pH "valuatwhicli calcium tinuous control of the amount of added 'coagulant '4.*Th PIOCeSs asset" forth in'clan I inwhich i y the coagulant'is aluiriinuinsulphate.y

5.*A coagulation process comprising'mixing a raw `aqueousliquid' containing y"coagulable mate'- rialwith'faninilowof Water of lower pH so as to lowerthe'resultantpH .of thel rnfiixtu're, 'further treating the mixture ofliquids with vsufll'cient'car-V 'terminating' said'carbon' dioxide treatment and then addin'ga 1 coagulant acting further to lower v f 'the pHvalue of the liquid 'so that it is 1.0 or-more where the raw solids from the secondary clarifier below 1said pH value at 'which calcium carbonate y can exist iii equilibrium in said liqud'and effective tc cause ccagiatic'ncfmateriai 'in'saiq liquid i to clarify the'liqui'd to desired-degree.

y f l JOHN 

